


The Experiment - A Gumrob/Robball Fanfic

by Cyan_Sky1



Category: The Amazing World of Gumball
Genre: Blow Jobs, Come Inflation, Cum Inflation, Developing Crushes, Face-Fucking, First Time Blow Jobs, Gumball just wants sex tbh, Hate Sex, Hate to Love, Inflation, Love/Hate, M/M, Oh yeah we’re getting into the weird shit, Rob is a cunt at first but he CUMS around hahahahaha I’m funny, Science Experiment, Science Experiments, Sexual Experimentation, ambiguous ending, navel fucking, navel squirting, wow there’s a lot of cum inflation, yes you read that right there’s navel fucking
Language: English
Status: Completed
Published: 2018-08-02
Updated: 2018-08-02
Packaged: 2019-06-20 14:34:35
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings, No Archive Warnings Apply
Chapters: 1
Words: 4,555
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/15536376
Author URL: https://archiveofourown.org/users/Cyan_Sky1/pseuds/Cyan_Sky1
Summary: Gumball is promised to be paid a ridiculous amount of money to participate in a mystery sex-related experiment run by scientists that have been kept anonymous. All he plans to do is bang whatever girl he’s supposed to, grab the money, and get out. But what happens when the person he’s supposed to bang is actually his arch nemisis? And wait, why did that robot thing give him a shot in his stomach...?





	The Experiment - A Gumrob/Robball Fanfic

**Author's Note:**

> Look man I forgot to mention I headcannon when Rob cums his penis glitches so please imagine that while reading please and thank you

he entire building, and even the door right in front of him, was a strange tiled-like textured baby blue. It was quite a strange sight to see a building and even everything inside the building to be such a random pastel color, but considering how much they said they would pay Gumball Watterson for this so called ‘experiment’ has definitely helped to chase away any worry in his mind. These group of scientists said that the company’s color was baby blue, and they thought the blue cat would be the perfect honorary test subject for their final product. They hope they won’t have to do anymore testing after this, but what makes Gumball especially excited is that they said it had something to do with sex. However, there was a catch: ....he couldn’t jerk off for a month before this day arrived. Back when they offered him the deal, he originally said no way, he didn’t want to not be able to jerk off for a month! But then they told him he would be paid 100,000 dollars if it was a success, and well....let’s just say that was an excellent motivator to not touch himself the past four weeks. And as promised, once the month was up, they gave him a free ride to the scientist’s testing building, and was sent to this very door. The problem is, now he’s right in front of the door, and he’s feeling an awful lot of anxiety now. They said once that he opens this door the experiment will begin. He has no clue what may actually be behind the door, all he knows is it’s gonna be something sex related and he may end up naked and a months worth of cum will most likely be milked out of him. That last thought stirred his dick to life already, which also reminded him how desperate he is to jerk off already. So really, he should just get this door opened to get this experiment done and over with, get his money, and go home rich and happy because he finally got his much needed sex.

And with that, Gumball opened the door, and braces himself for the worst.

“Hello, Gumball Tristopher Watterson.” A small Bobert-like looking android but with no legs and a tiny jet back that helps him fly hovers towards Gumball as he closes the door behind him.  
“You are test subject #423, and hopefully our very last test subject for our product, The Inflator. You are going to be given a shot in your stomach that will make your stomach more flexible and suitable for holding more fluids.”  
“Wait, what-OW!” Without any other warning, a different robot arm that came from the nearby wall lifts up Gumball’s sweater and injects him very quickly and swiftly with said given shot the hovering robot hastily described to him before he could even process what the robot just said. 

He feels the shot’s serum shoot into his system, and feels his stomach, in a strange way, loosen up, along with his hips and butt. He looks down at himself and sees nothing has changed, but he feels lighter somehow. Along with these strange sensations, his head feels like is buzzing with energy. After a minute or so he feels all of that energy in his head launch into his entire body, and it sends a shiver down his spine. As quick as a lightning strike though it goes away, and the robot speaks again.

“Congratulations, the serum has successfully been ejected into your system without any complications and you may now go on to meet subject #422. Both of you will know this bit of information, but your primary objective is to have intercourse until your partner feels satisfied. Do not be alarmed if your stomach, subject #423, swells up, for it is supposed to do that. Now I will put up the wall in front of you which will reveal your partner for this experiment, and a wall will go down behind you as well so I, nor anyone else, and interfere. If anything goes wrong please note there are hidden cameras in this room and scientists in the room next door monitoring what is happening and is prepared to assist you if there is an emergency. Thank you for participating in this experiment, and you will receive your money afterwards. Have fun.”  
And before Gumball could ask any questions, the wall that the robot described swiftly and quite loudly falls behind him, and he senses that another wall that was in front of him did the same thing. He closed his eyes and covered his face with his forearms out of habit, but when he heard the wall in front of him go up, he slowly uncovers his face and opens up his eyes.

It takes a second for his eyes to adjust to the light again, but when his vision is restored he cannot believe who is in front of him.  
“R-Rob?!”  
“GUMBALL!” Almost Immediately the tall cyclops in front of him narrows his eyes and grits his teeth at seeing his most hated nemesis in front of him. He temporarily forgets about the experiment and lunges forward to strangle the blue cat, which quickly causes the two of them to fall on the floor in a rumble.  
“URGH! R-Rob-ack!-Wait!” Gumball tries to reason with Rob, and without any warning the two of them hear a voice over the speakers implanted in the room  
“If you two cannot behave and continue with the experiment, then I’m afraid we will have to cancel and not give you two your desired money. And Rob, I have a feeling you won’t be able to survive another five minutes if you don’t get rid of your...little problem we made for you to solve down in your pants~.”  
“Y-Yeah Rob we’re s-supposed to...wait...what did they do to you?” The blue cat’s eyes shifted down to look at Rob’s said crotch area, but can’t really see anything due to the hard, solid nature of his shorts.  
“I-erm...um...” The cyclops shivered for a second, and takes his hand off of Gumball so he can get up first. The blue cat notices Rob’s cheeks look like a much more darker grey then they usually are, and realizes he’s blushing. After they’re both standing for an awkward moment, Rob’s breaks the silence with a scoff.  
“Ugh, why are you even here anyway? Don’t you already have a house with your family and stuff?” Rob tsks and looks away from Gumball after a moment, hunching over slightly and crossing his arms.  
“Well yeah, but we really need the money. We’re honestly a super poor family and we need all the help we can get. Why uh....why do you need the money?”  
“Uh, because I DON’T EVEN HAVE A HOUSE?!” The cyclops snapped and turns to look at Gumball again.  
“This is literally the only chance I have for finally getting some shred of a normal life with a actual house, and yet here you are trying to ruin it again-“ Rob stops and actually thinks about what Gumball said earlier.  
“You’re....you and your family are actually poor?”  
“Dude we’re so poor charity donates to us.”  
“Oh.” The cyclops stops to bite his lip in thought, and looks down at the floor. He appears to look guilty for what he said.  
“I um....I’m sorry, Gumball. I never knew that.”  
“Dude it’s ok. Can we have sex now?” Gumball smiles and flicks his tail teasingly, but for some reason it brings out something almost primal like in Rob, and before Gumball could think Rob grabs him by the collar of his sweater and kisses him right then and there.

Gumball’s feet were off the ground, and wow he had no idea Rob was this strong. Or maybe he’s just that light. Either way, right before he can register or melt into the kiss he hears the cyclops very suddenly moan.

“I-I need to take these off, this is starting to really get to me.” Rob sets down the blue cat without another word, and glitches out of his shirt and pants.  
The blue cat was left breathless as his slim static figure, and looking down he finally realizes what the scientist and Rob was talking about.

He must have been ejected with some kind of serum, because his balls looked like they were ten times their normal size and they looked awfully swollen and heavy and god that looks like it’s painful....

“You gonna help or are you gonna stare?” Rob says with this tone of voice that sounds slightly strained, and when Gumball looks back up to see his face he can tell that the balls are really starting to effect him by the way his cheeks were flushed and the way he was looking at him.  
“Erm....a-alright....” the blue cat comes closer to Rob, and begins to undress. 

He hears the cyclops take a sharp inhale through his teeth when his bare chest was shown, and show his legs tremble a little when he took off his pants and underwear as well. But when he looked back up to Rob again when he was finished, he felt himself start to feel weak in the knees and feel aroused again as well.

It seems that the serum triggers the both of them to get more aroused when they look at each other naked.

“Ugh, fuck these scientists.” Gumball murdered out loud as he got on his knees and grabbed the cyclop’s penis without any warning.  
“Shit-Gumball!” Rob grabs the said cat by the ears and thrusts his pelvis right into his face, the cyclop’s balls slapping his cheek. It takes him a second or two to register what he just did, and let’s go of Gumball’s ears again.  
“Oh, sorry! I-I think the serum made me really sensitive to touch down there too-“  
“-Shut up and treat me rougher.”  
“What?” Rob looks down to look at Gumball, only to see a devious look in his eyes.  
“You’re my enemy, right? Then treat me like it~”

Rob never thought he would be in this position. He always thought he would be a caring and loving guy during sex, but in this very moment Rob wanted nothing more then to break Gumball like the fucking brat he was.

So Rob gave into Gumball’s commands, and shoves his dick right into Gumball’s mouth without a second thought. The blue cat gasps and chokes on his dick, but tries his best to take it all in and swallow it down his throat, which he somehow succeeds in. The cyclops smiles evilly, and proceeds to grab the cat on his fur and yank it up and down his cock roughly. He face fucks Gumball, right then and here. He can hear him gasp for air and moan, and then he can feel his paws gripping him by his legs and holy shit he has claws.  
Gumball continues to sputter and whine, but it is of no use. Eventually he gives in and lets him self close his eyes, and get lost in the feeling of his throat being so abused. Rob’s swollen balls continue to hit Gumball on his neck, which has a noticeable bulge where Rob’s dick is inside. The cyclops is very clearly close as he keeps on grunting and panting, nearly breathless it sounds like, and for the final blow Gumball opens up his eyes again and gives Rob a pleading, puppy eyed look. A silent beg to cum inside his throat. Rob makes a loud moan, it almost sounds like he’s screaming, and the load of cum goes down Gumball’s throat. The blue cat struggles to keep up with the spurts of white liquid, but Rob doesn’t seem to mind watching as Gumball’s cheeks swell up occasionally, and some cum dribbles down his chin. The blue cat finally finished swallowing it all and slowly takes his mouth off his dick to check if his balls still looked swollen, and he was surprised to see he was still rock hard. A crackle can be heard, and then the previous scientist’s voice comes over the intercom:

“If you want to relieve all of the cum he has inside of him, I recommend you let him fuck you Gumball. He’s going to need to do it quite a lot of he’s going to be relieved any time soon.”  
“Oh shit...” Gumball muttered to himself in an almost scared tone as Rob leans down and grabs the blue cat by his torso, and without any further questioning forces his ass into taking his member inside of him, still slobbery and wet from the blowjob.

He literally grabs and uses him like he’s his own personal fleshlight, and for some reason it’s the hottest thing alive to Gumball. His ass was burning from the abuse, and he was screaming and begging with incomprehensible words, but he didn’t care. Somehow, this reached his deepest level of desires and he didn’t dare want to stop yet.

Another grunt from Rob tells him that he’s about to cum, and right on cue the cyclops hold Gumball up by his arms and squeezes them hard, and suddenly the blue cat’s back was against Rob’s chest and he’s cunning and he won’t stop. He looks down with blurry eyes to see that his stomach was beginning to swell up like the robot said he would, and that feeling of lightness has returned, only he doesn’t feel as light as he used to anymore. However something inside him told him that the weight felt better then the lightness ever could, and he needed more weight.

So the blue cat managed to elbow Rob in the stomach hard enough for him to fall over, and Gumball uses his moment to get up, turn around, and land back on his dick cowgirl style. He looks hungrily into the cyclop’s eye as he begins bouncing, and the look of hurt and hatred on Rob’s face when Gumball elbowed him to knock him down on the floor melts into one of pure pleasure. The burning pain that the blue cat felt from the first fuck is all gone now, and he can only feel the good parts of sex he heard so many things about now. He can barely think, barely even comprehend what he was doing to Rob. All he could do was bounce up and down on the cyclops dick, and feel as amazing as he does now. 

While Gumball bounces on him Rob decides to tease him and help him along, by reaching up to feel the small bulge that has appeared on the blue cat’s stomach. The fur is soft and sleek, he obviously tried his best to clean himself for this sex experiment. He can feel the soft small buns of Gumball’s nipples, and he can feel the baby fat he still has on his sides. Adorable. He then finally moves on to feel the small bump that comes from inside of Gumball, and was surprised by how it felt. It was soft and squishy, most likely because it’s all made from cum. ...HIS cum. Oh god, it’s his cum inside of Gumball right now, and he’s about to give him so much more...

Rob makes another noise of pleasure along with Gumball’s constant meows and moans, and grabs him by the hips again to thrust along with him. The thrust at the same time, and he must have hit his prostate because Gumball is screaming now and he’s spraying cum all over his chest and his ass is clenching his member around him and it’s so tight it almost hurts. Rob screams along with him and cums even more inside of him, and the size of the blue cat’s stomach increases to about the same size of a small soccer ball. 

But they’re not done. God they’re not done. The blue cat slowly stands back up, holding his stomach with his hand, and then lays back down on his back, with his legs spread wide open, his asshole slightly agape and some white can be seen inside. They’re both panting heavily now, and both of their nerves feel like they’re on fire. Rob grunts as he gets up, and then puts both of his hands on either side of Gumball’s head, taking a moment to just try and catch their breaths.

“Rob...Rob please....I need it...!” The blue cat begins to whine and thrust his lower body to try and meet the cyclop’s crotch, but he lifts up just in time before his stomach or his crotch could touch him.  
“Careful, Gumball. I don’t know if touching your stomach is the best thing right now...” Rob feels his dick throb and twitch despite what his rational part of his mind was trying to reason.  
“Rooooob! God, you’re so good baby! Please! I need you to fuck me one more time, please!” The cyclops shivered when he begged for him like that. And did he just call him baby...?

Meanwhile, Gumball is beyond wanting any kind of reason. He wants to be fucked, right here and right now. Almost all of the lightness feeling is gone, and he’s so full, so *full*. But he still wants so much more, he’s begging for more now. He can’t wait any longer, his mind is so scrambled with blind lust. 

Eventually Rob decides to give in and slowly pushes his dick inside Gumball’s ass one more time, and the whines of desperation quickly became moans of pleasure. And when Rob looked down at Gumball at that moment, the way that his ass felt around him and the way that cute little nose scrunched up when he moans, and they was his eyes screw shut, and how his fur is messy and tousled with all of the sex they did, something stirred within him. The cyclops no longer felt like he was fucking his enemy. He was so clearly fucking so much more. Someone that was able to unleash the animal inside of him, unleash the pure unrelenting fire that he so often hides within his soul. He let’s it all out for him. He doesn’t even realize that he’s thrusting full and deeply into Gumball until he noticed how his belly jiggled in time with his thrusts, and the blue cat opened up his eyes again to look at him. 

Gumball’s head began to unscramble again as he’s finally getting what he wanted, and he looks at Rob and notices how cute he actually is. His static skin is shiny, almost glossy, and yet when he reaches up to touch it it feels soft, almost exactly like actual skin. He also notices with his paw on his arm, that a faint glow inmates from his static skin, like a soft glow from a actual television skin. The blue cat looks up at his face again. His cheeks are a very dark shade of grey now, and his yellow tongue is building up saliva and he has that gleam in his eye that whenever Gumball looks in it he can’t help but feel his stomach do a somersault, and he can tell it’s not just the cum inside his stomach right now. Oh god, the cum inside of his stomach...!

The blue cat lets out a high pitched whine, and pulls Rob closer so he can wrap his arms around him. Rob’s chest meets with his stomach and the cyclops cringes thinking he may have hurt him, but instead the blue cat keeps on putting and moaning. He’s...ok? The cyclops tests his limits and puts one hand on one of the cat’s hip, and the other, soft pink hand, on top of his stomach and feels it again like he did earlier. All of the softness is almost gone, and it feels like a giant swish of liquids inside of him. It feels warm, and Gumball seems to really like it when he pets his swollen tummy full of cum. So he takes it to the next level and carefully leans down a little while he keeps on thrusting, and gives his tummy a little kiss.

“Awahh...Rob~! Please do more of that! A-And go harder!” Gumball spoke up in between a mixture of meows and moans. Rob smiles at the plead, and does as he’s told.

The cyclops starts to slam his penis into the blue cat’s hole while teasingly kissing and licking his stomach, and Gumball is very clearly enjoying it because his ass is clenching around him really hard now and nearly screaming again, and his voice has gone raw and yet he still has so many sounds left to make for him. All for him. No one else but him. Rob moans again, loud and hard, and shit he wants so badly to go a little longer. Just a little longer, god he never wants this moment to end! 

And a final blow, Rob thrusts his entire length into Gumball, balls deep, then leans over and kisses him again right then and there. That was it for the both of them, and Gumball screams again as he cums, spraying it all over his cum swollen tummy and Rob. Rob just bursts and cums in Gumball as much as he could right then and there. He watches in pure fascination as the cum filled tummy grows bigger and bigger and bigger, slowly and surly, until something neither Gumball or Rob expected happened. 

Cum spurted out of Gumball’s navel, and it makes Gumball throw his head back, arch his back, and scream in more pleasure. The sight makes Rob hard all over again, and he gets a wicked idea. Rob takes Gumball’s stomach and squeezes, and sure enough more cum spurts out of his belly button. 

“OH GOD ROB IT FEELS LIKE I’M EXPLODING~!” Gumball pleads with the cyclops, to stop or keep going the cyclops doesn’t know, but either way he stops in his tracks when he sees the blue cat’s navel open up, almost as wide as his gaping asshole was earlier, and the only thing Rob could think of right then in there was to stick his dick in it. So he decides to do just that. 

Rob yanks his dick out of Gumball’s hole, and notes that the blue cat just leaves his legs spread open and his arms out on a t-pose like position on the floor, heaving breaths but still looking at the cyclops, watching for what he was about to do next. Rob puts both of his feet on each side of the blue cat, positions his penis, and squats down until his dick was inside Gumball’s belly button. His navel, as Rob expected, felt wet from the cum it spurted out earlier but still tight and warm and not like anything he’s ever felt like before. He smiled while looking down at the cat, let himself down on all fours so his dick can stay inside and he can thrust easier, and began pushing and pulling his dick in and out of his little navel. He’s never felt so relieved in that moment to have a tiny head and a big shaft near the end, so he can at least put it in halfway through. Halfway is all he needs.

Meanwhile, any and all previous thoughts he could even comprehend as he finally got all of the lightness feeling away is completely fried and gone now. The only thing he could focus on, the only thing he could feel, was that his stomach felt like it was gonna explode with each thrust Rob gives to his belly button. And yet...he feels more alive then ever. How has he never had sex with Rob before? He very clearly knows everything that could possibly make him crazy, and he knows he’s gonna be sore for days, possibly even weeks, but he still loves it. He.....he thinks he loves *him.*

Rob very clearly couldn’t last any longer though, and he cums one last time, the cum spurting into the belly button but there wasn’t enough space for it to hold it all so it all comes flying out, and Gumball cums again in turn and he feels some leak out of his gaping asshole too. And then without any warning, Rob collapses on his side, right next to Gumball, and the two pass out on the floor covered in cum.

The scientists see this, and bring out their special vacuum bot. The vacuum bot slowly rolls out into the scene, and sticks it’s hose right into Gumball’s ass and slowly but surly sucks all of the cum out inside of him. The scientists watches though the camera as Gumball’s stomach slowly deflates back to it’s normal size, but his skin looks stretched out and very obviously irritated from all of the sudden stretching and deflating. So they get that robot arm to give him another shot, a shot that gets rid of the stretch marks and flabby skin. There, now he has a normal stomach again. Now for Rob. His balls have shrank back to their normal size again, but they still look overall very irritated, so the robot arm gives him another shot in his pelvic region and watch as the irritation goes away. Then the vacuum bot sucks up all of the remaining cum off the two boys, and cleans up the area if cum around them. Finally, the scientists order their body guards and nurses to pict them up and properly clean and groom them.

After they were cleaned and back into their clothes, they drag the two still unconscious boys back to the main building’s hall and memory swipe them before they go. That way they can keep their experiment secret, and any and all trauma they may have endured during the experiment has been erased from their minds and all they know is a midi ale has happened and they were each sent 500,000 dollars as promised. The scientists fist bump as the boys are dropped off to their original places.

—-

Rob hides in the bushes, waiting for Gumball to round the corner to see him with Penny again. The two are holding hands, and the blue cat is smiling. Like he doesn’t remember anything that happened.

Rob realized that as soon as he was unconscious the scientists must have attempted to wipe his memories and just give him the money and pretend it was a miracle that bought it to him, but he was no fool. He was smarter then they realized if they think they could ever wipe any of his memories away. However, as sad as it is to say it...it looks like they got Gumball’s memories successfully wiped. So he doesn’t remember the amazing sex they had. How it felt when Rob came inside of him so many times, and how he looked when he was screaming his name, and how he looked with that creamy white cum all over his fur.

He has no idea, but for some reason he feels this strange attraction to Gumball now. He wonders if he can feel it too...

**Author's Note:**

> Wow I’m into some kinky shit


End file.
